Dolby Pro Logic/Pro Logic II is a matrix decoder which can derives surround sound (into 4 channels- DPL/5 channels - DPL II) from any stereo source.
Dolby Digital simply does transmitting. On DVd, usually it's 5.1. That means the sound source has 5.1 discrete channel sound tracks and Dolby Digital keeps each channel separated throughout the decoding process.
Greg: As coolposter notes, there is a separate channel for everything in 5.1. This really makes a HUGE difference. 5.1 surround effects can jump from speaker to speaker and swirl aorund you until you sometimes think you are turning too! And when it comes to bass, the .1 low frequency effects channel (LFE) puts out MUCH more boom than plain old Pro Logic.
If you can, go to a good dealer and have them give you a 5.1 demo from something like Lord of the Rings. You'll hear it!
HAN hit the nail on the head. The differences between pro logic and DD5.1 are HUGE and easily perceivable to even the casual listener. Especially in movies that have been done as well as LOTR or SW:EpII.
If you made this post because you have a pro-logic receiver, and you're on the fence about whether or not to take your Christmas money and spring for a DD receiver then let me help you out. DO IT. You will not be disappointed.
It's about as big as the difference between mono and stereo.
Because that's literally what you're getting. Instead of two rear speakers outputing the same (mono) matrixed sound, and a center that is derived from the L and R. You get five completely independant sources PLUS the ".1" all bass effects channel.
To my ears, the differences between 5.1 & 6.1 aren't nearly as dramatic as they are between DPL and 5.1. There is no question that 6.1 firms up the rear imaging and gives a more defined soundfield (IOW, I can hear a difference), but my 5.1 setups are very satisfying and I don't feel the itch to upgrade them...
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